Control of 5S RNA synthesis in Xenopus laevis

Abstract

PREVIOUS reports^1–3 have shown that somatic cells of Xenopus laevis synthesise a 5S RNA which differs in sequence from 5S RNA synthesised by oocytes. In none of these reports is there any indication of ovary-type sequences being synthesised by somatic cells. Moreover, although the oocyte 5S sequences are heterogeneous, the somatic sequence is essentially homogeneous. We report here that X. laevis liver cells labelled in organ culture do not detectably synthesise ovary-type 5S RNA sequences but find that a transformed tissue culture cell line, derived initially from somatic kidney cells, synthesises significant (10–20%) amounts of ovary-type 5S RNA sequences. Taken together with the observation that some 5S genes are translocated to a novel site adjacent to the nucleolar organiser in these cells⁴ this result is important for an understanding of the nature of differential control of 5S gene transcription in X. laevis.